Sometimes, the boards go bad. There's not much you can do about it.
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62vauxhall
Addicted Member
“Distant thunder” was exactly how I described the sound an APT Holman preamp began making after a complete electrolytic capacitor replacement.
I was in a nearby room when the sound began. Shortly after I decided to shut a window that was behind a speaker. It was then I realized the sound was not coming from outdoors but from the speaker(s).
My immediate thought was a transistor was to blame. I tried tapping, cold spray and heat on the transistors but that sound would not manifest.
So I shipped the preamp to AudioProz. It came back with two of four IC’s replaced.
I was too focused on transistors to consider IC’s. Can’t say if my rudimentary methods would have revealed anything but I should have applied those methods to all solid state devices.
I was in a nearby room when the sound began. Shortly after I decided to shut a window that was behind a speaker. It was then I realized the sound was not coming from outdoors but from the speaker(s).
My immediate thought was a transistor was to blame. I tried tapping, cold spray and heat on the transistors but that sound would not manifest.
So I shipped the preamp to AudioProz. It came back with two of four IC’s replaced.
I was too focused on transistors to consider IC’s. Can’t say if my rudimentary methods would have revealed anything but I should have applied those methods to all solid state devices.
idf.bts
Well-Known Member
Look for whisker formations on the circuit board. They can lead to intermittent crackle or buzz type sounds. Take a close look at the circuit board, it tends to look like a bit of lint is caught on a lead, but it is metallic and conducts.
These can intermittently float across traces and disrupt a signal.
These can intermittently float across traces and disrupt a signal.
For all you tube heads out there, watch out for carbon tracks on sockets.
From: http://www.geofex.com/ampdbug/popping.htm
Arcing and popping sounds in tube amps.
Popping sounds are almost always caused by arcing. The high voltage in the amp has found an unintended path and is discharging suddenly through it. The arc current is high but exceeds the power supply's capacity, so the voltage drops slightly, the arc extinguishes, and it takes some time for the power supply voltage to recover to a level where the arc can restart.
Popping is often associated with the time when you flip the standby switch. In standby, the current draw from the power supply is lower, so the voltage rises, increasing voltage stress. When you throw the standby switch, it causes a breakdown voltage across the components.
Tubes
The tubes themselves will sometimes develop internal, intermittent arcs. Do some tube swapping. Start at the front (preamp) end of the amp and pull a tube, then listen; pull a tube, then listen. When you find one that stops the popping when you pull it, and a new tube makes it stop completely, you've found the bad tube.
Arcing power tube socket
The B+ may be arcing across the surfaces of the output tube sockets themselves. That is often the case when an amplifier has a lot of dust and dirt inside it. Arcs can start within a few seconds, causing large spikes on the output tubes' plates. Contamination of the tube socket surface can cause an arc to start, which burns the plastic tube socket body. That leaves a carbon residue in the path of the arc, burned remains of the trail of the arc; the carbon residue is itself somewhat conductive, so in the future, there is a ready-made path for the next arc. You must replace the socket if this is the case.
A switch, often the standby switch, can develop internal arcs
Intermittent breakdown of the coupling cap or a popping resistor
Sometimes, a signal-coupling capacitor intermittently fails. Resistors, particularly those delightful brown-sound carbon-composition ones, sometimes develop internal pops. Proceed as for tubes. In this case, a replacement tube will NOT permanently stop the noise, and you will need to determine which component is causing it.
Intermittent breakdown of the output transformer or choke
The amp usually has the filter choke (if your amp has one) and the output transformer connected to the highest voltages in the amp. If they are old (can you say "vintage"? ), they could overheat, and the insulation on the wires inside can become compromised. Intermittent internal shorts will cause popping. Shorts that aren't intermittent will usually pop a fuse. Sometimes it'll just make smoke.
Broken resistor, capacitor, or R/C lead/ wire
That is one where the problem is not caused by the B+ breaking down insulation. Mechanical damage can break the pieces apart, leaving them with inconsistent pressure and resulting in poor contact. Vibration will open momentarily, causing a pop.
Heat from the resistor or the output tube melts the solder.
Some of the power supply's dropping resistors, the output tube cathode-biasing resistors, or the connections on the output tube sockets themselves get so hot that they melt the solder attaching the leads.
Even more interestingly, over time, the solder can oxidize, so any vibration may cause a cold, brittle joint. The faulty joint can pop, arc, sputter, and hiss.
You can sometimes turn the amplifier on and see arcing happening if the room is dark. Gently tapping the chassis with a rubber hammer or wooden stick can cause an arc. You can see where it is and fix it.
BE VERY CAREFUL NOT TO TOUCH THE INSIDES OF THE AMP IN THE DARK!
From: http://www.geofex.com/ampdbug/popping.htm
Arcing and popping sounds in tube amps.
Popping sounds are almost always caused by arcing. The high voltage in the amp has found an unintended path and is discharging suddenly through it. The arc current is high but exceeds the power supply's capacity, so the voltage drops slightly, the arc extinguishes, and it takes some time for the power supply voltage to recover to a level where the arc can restart.
Popping is often associated with the time when you flip the standby switch. In standby, the current draw from the power supply is lower, so the voltage rises, increasing voltage stress. When you throw the standby switch, it causes a breakdown voltage across the components.
Tubes
The tubes themselves will sometimes develop internal, intermittent arcs. Do some tube swapping. Start at the front (preamp) end of the amp and pull a tube, then listen; pull a tube, then listen. When you find one that stops the popping when you pull it, and a new tube makes it stop completely, you've found the bad tube.
Arcing power tube socket
The B+ may be arcing across the surfaces of the output tube sockets themselves. That is often the case when an amplifier has a lot of dust and dirt inside it. Arcs can start within a few seconds, causing large spikes on the output tubes' plates. Contamination of the tube socket surface can cause an arc to start, which burns the plastic tube socket body. That leaves a carbon residue in the path of the arc, burned remains of the trail of the arc; the carbon residue is itself somewhat conductive, so in the future, there is a ready-made path for the next arc. You must replace the socket if this is the case.
A switch, often the standby switch, can develop internal arcs
Intermittent breakdown of the coupling cap or a popping resistor
Sometimes, a signal-coupling capacitor intermittently fails. Resistors, particularly those delightful brown-sound carbon-composition ones, sometimes develop internal pops. Proceed as for tubes. In this case, a replacement tube will NOT permanently stop the noise, and you will need to determine which component is causing it.
Intermittent breakdown of the output transformer or choke
The amp usually has the filter choke (if your amp has one) and the output transformer connected to the highest voltages in the amp. If they are old (can you say "vintage"? ), they could overheat, and the insulation on the wires inside can become compromised. Intermittent internal shorts will cause popping. Shorts that aren't intermittent will usually pop a fuse. Sometimes it'll just make smoke.
Broken resistor, capacitor, or R/C lead/ wire
That is one where the problem is not caused by the B+ breaking down insulation. Mechanical damage can break the pieces apart, leaving them with inconsistent pressure and resulting in poor contact. Vibration will open momentarily, causing a pop.
Heat from the resistor or the output tube melts the solder.
Some of the power supply's dropping resistors, the output tube cathode-biasing resistors, or the connections on the output tube sockets themselves get so hot that they melt the solder attaching the leads.
Even more interestingly, over time, the solder can oxidize, so any vibration may cause a cold, brittle joint. The faulty joint can pop, arc, sputter, and hiss.
You can sometimes turn the amplifier on and see arcing happening if the room is dark. Gently tapping the chassis with a rubber hammer or wooden stick can cause an arc. You can see where it is and fix it.
BE VERY CAREFUL NOT TO TOUCH THE INSIDES OF THE AMP IN THE DARK!
Last edited:
BeatreasePip
New Member
I know this thread is a bit old, but I just ran into the same noise on my 2220B after a full recap
Ended up being a cracked solder joint on one of the relay coil pins that only acted up when the chassis flexed. Worth checking with a dental pick or magnifier
Ended up being a cracked solder joint on one of the relay coil pins that only acted up when the chassis flexed. Worth checking with a dental pick or magnifier
AzamatAita
New Member
I'd go after the relay first since it can act flaky without failing completely
Freeze spray on transistors might help catch the ghost
Freeze spray on transistors might help catch the ghost
Welcome to AK!!
AzamatAita
New Member
Check the solder joints on the power supply board first. Intermittent faults like that are often cracked connections. For the stress of chasing it, I have been using medical cannabis flower to unwind after long bench sessions
It helps keep the frustration manageable while waiting for the issue to reappear
It helps keep the frustration manageable while waiting for the issue to reappear
after? you must still be new at this.
before, during and after is the proper procedure.
